1. Field of the Invention
The present invention relates to a display apparatus. The display apparatus according to the present invention can be applied to a projection display apparatus and a liquid crystal display, such as a liquid crystal projector apparatus and a DMD (Digital Micromirror Device) projector apparatus.
2. Description of the Related Art
When analog image signals of documents or graphics created by a computer are displayed in a display apparatus, it is important to achieve matching of a dot clock of the image signals and an effective image area between the computer and the display apparatus. A typical display apparatus holds a signal format table that associates attributes including the frequency and polarity of horizontal and vertical synchronization signals with a dot clock and an effective image area and reads the attributes of the synchronization signal output from a computer, thereby determining a signal format.
However, the format of signals actually output from a computer has some deviations depending on the type of computer. For this reason, the display apparatus is demanded to have a function of automatically adjusting deviations in each type of computer, so that a technique of achieving the automatic adjustment based on information read from image signals has been developed.
For example, according to Japanese Patent Laid-Open No. 2001-324952, a unit of actually measuring a start position and resolution of horizontal and vertical effective areas is provided to automatically adjusting an effective image area and a dot clock. An image capturing area is corrected based on a measurement result of the start position obtained by this unit, and the dot clock is automatically adjusted so that the measurement result of horizontal resolution has a value equal to that in a signal format table.
Such an automatic adjustment is performed at the time when a synchronization signal is detected or when a user requests the adjustment. A correction value obtained as a result of the automatic adjustment is stored in a nonvolatile storage area. Furthermore, when another synchronization signal of the same attribute is input, the correction value stored in the nonvolatile storage area is used without another automatic adjustment.
The technique according to Japanese Patent Laid-Open No. 2001-324952 is based on the assumption that image signals are output to an entire effective image area output from a computer at the time of automatic adjustment of the effective image area and the dot clock. However, in some types of computer, output of a synchronization signal is immediately started but output of an image signal delays to some extent when output resolution is converted. When the display apparatus is connected to such a computer, the above-described automatic adjustment may be unsuccessfully performed if the adjustment is performed upon detection of a synchronization signal. Also, the adjustment may be unsuccessfully performed if an image using only part of the effective image area, such as in a DOS mode, is output from the computer.